Fix schema equality for empty schemas and identifier fields (#3958)

* Fix schema equality for empty schemas and identifier fields

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Use loops for schema equality regression cases

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Keep schema equality tests focused on regressions

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: kevinjqliu

pyiceberg/schema.py

@@ -115,16 +115,13 @@ def __len__(self) -> int:
 
     def __eq__(self, other: Any) -> bool:
         """Return the equality of two instances of the Schema class."""
-        if not other:
-            return False
-
         if not isinstance(other, Schema):
             return False
 
         if len(self.columns) != len(other.columns):
             return False
 
-        identifier_field_ids_is_equal = self.identifier_field_ids == other.identifier_field_ids
+        identifier_field_ids_is_equal = set(self.identifier_field_ids) == set(other.identifier_field_ids)
         schema_is_equal = all(lhs == rhs for lhs, rhs in zip(self.columns, other.columns, strict=True))
 
         return identifier_field_ids_is_equal and schema_is_equal

tests/test_schema.py

@@ -119,6 +119,18 @@ def test_schema_repr_two_fields() -> None:
     assert expected == actual
 
 
+def test_empty_schema_equality() -> None:
+    assert Schema() == Schema()
+
+
+def test_schema_equality_ignores_identifier_field_order() -> None:
+    fields = (
+        NestedField(field_id=1, name="foo", field_type=LongType(), required=True),
+        NestedField(field_id=2, name="bar", field_type=LongType(), required=True),
+    )
+    assert Schema(*fields, identifier_field_ids=[1, 2]) == Schema(*fields, identifier_field_ids=[2, 1])
+
+
 def test_schema_raise_on_duplicate_names() -> None:
     """Test schema representation"""
     with pytest.raises(ValueError) as exc_info: